SIROFLO®
fumigation technology was invented in Australia in the 1980's, for the purpose
of fumigating grain in bulk using gaseous phosphine. Until recently the
technology has been adopted in relatively few other countries because of
the difficulties associated with the registration of gaseous phosphine products,
despite the fact that their active ingredients are chemically identical
to the less pure solid phosphide formulations that are in common use worldwide.

However In the last two years, significant
moves have been made to broaden the international market for SIROFLO® technologies and gaseous phosphine
products. Grain Tech Systems Pty Ltd (GTS) is a small Australian company
that has participated in this process by introducing the technologies to
the People's Republic of China.

This paper briefly describes some of the projects
that have been undertaken by GTS in China, and some of the emerging grain
fumigation technologies that are being developed in competition with GTS.

Introduction:

SIROFLO® fumigation
technology was invented by Dr Bob Winks of CSIRO, Australia, in the early
1980's and was developed for the fumigation of grain using a gaseous mixture
of Phosphine and Carbon dioxide. In Australia this fumigant mixture is sold
under the registered name ECO2FUME®. The fundamental aim of SIROFLO®
technology is to deliver and maintain a low concentration of phosphine throughout
a grain mass for an extended period of time in order to maximise the toxic
effects of the phosphine fumigant.

By creating and maintaining low PH3 concentrations over extended time periods, the use
of SIROFLO® technologies not only increases the effectiveness of
the fumigant, but also significantly reduces the quantity of fumigant used
in a fumigation, and thus minimizes emissions into the environment. At the
same time, overall safety for fumigators and silo operators is enhanced
since there is no direct contact with the fumigant. Fire hazards are eliminated
and emissions from storages during fumigations are greatly reduced. Phosphine
residues in the grain are also significantly reduced when using these technologies.

The SIROFLO® group of technologies
fall into three categories:

SIROFLO®
for fumigation of non-gas-tight storages;

SIROCIRC®
for recirculatory fumigation in partly gas-tight storages;

SIROFUME®
for one-shot fumigation of fully-gas-tight storages.

All three technologies carry international
patents, and are licensed to Cytec Industries of the USA, under a 10 year
agreement signed in 1999.

SIROFUME®
differs from the other two in being a "one-shot" technique in
which gaseous phosphine is dumped into a sealed storage. It will not be
discussed further in this paper.

SIROFLO®
involves the mixing of ECO2FUME® in air at a predetermined concentration, and blowing it continuously
at a controlled rate through the grain mass under a low positive pressure
using a small fan and distribution ducting.

Provided the walls of the storage are reasonably
gas-tight, the low positive pressure ensures that fumigant leaks outwards
through the storage structure, and minimizes ingress of air such as could
locally dilute the fumigant concentration.

SIROCIRC®
is identical to SIROFLO® except insofar as it incorporates a return
duct connected between the storage roof and the fan inlet. This allows
the recovery of phosphine from the headspace above the grain and its recirculation
through the grain mass. In a reasonably well-sealed storage >90% of
phosphine can be reused.

Whilst SIROFLO® is a set-and-leave
operation, SIROCIRC® requires a reduction in the fumigant flow-rate
once phosphine begins to recycle back from the top of the storage. This
can be done manually, but control is facilitated by the use of an automatic
electronic controller that intermittently adjusts the fumigant flow to generate
a near-constant PH3
concentration in the delivery duct. The automatic microprocessor-based controllers
used in SIROCIRC® systems, were designed and developed by Len Cherkson
& Associates of Australia, and are manufactured by All-Systems Electronics
also of Australia.

Since most new storages in China are reasonably
gas-tight, GTS has concentrated on the development of a market for SIROCIRC®
systems incorporating automatic controllers with a manual over-ride. So
far GTS has installed 16 systems at eight sites and has contracts to install
a further 28 with expectations of further orders in the future.

GTS has also lodged an application with the
Ministry of Agriculture in Beijing for registration of the ECO2FUME® fumigant
mixture in China under the apt name "Yi Ke Fu" (meaning "easy
to kill insects"). GTS has also lodged an application for the registration
of VAPORPH3OS® (gaseous PH3)
under the equally apt name "Wei Ke Fu" (meaning "powerful
to kill insects"). Applications have been lodged on behalf of Cytec
Industries Inc of the USA, the global manufacturer and supplier of these
products. Both applications are expected to be approved in the immediate
future.

GTS's entry into the China market, and its
successful demonstration of a small SIROCIRC® systems near Beijing
in 1997, generated a much greater level of interest than expected. Since
then several Chinese companies have developed their own technologies for
fumigation of grain based on the use of gaseous phosphine, either derived
from cylinders or from on-site generators.

This paper briefly describes some of these
installations projects that have been undertaken by GTS in China, and some
of the emerging grain fumigation technologies that are now being developed
in competition with GTS.

Changping Demonstration Trial

With the help of CSIRO, BOC Gases and the
Beijing Central Grain Depot, and using equipment manufactured and supplied
by GasApps Australia, a demonstration SIROCIRC® system was established
at the Changping grain depot, near Beijing in 1997 for the purpose of demonstrating
the technology to anyone who was interested in seeing it, and also to obtain
test data to be used for the registration of ECO2FUME® in China.
The system was still in operation in late 1998 when the opportunity was
taken to invite participants at the IWCSPP conference in Beijing to see
it.

The demonstration trial was a temporary arrangement
and was built accordingly, using PVC pipework to deliver and recirculate
the fumigant through 12 x 600 tonne quite poorly sealed brick silos. Trials
were conducted using specially-bred phosphine-resistant insects placed in
cages inside the silos, to demonstrate the effectiveness of the technology
in delivering phosphine at constant concentration over a controlled period
of time. The results of these tests, together with smaller-scale tests conducted
in Guangzhou (south China) have been used in an application for registration
of ECO2FUME® in China.

Dalian Beiliang Grain Terminal is a new grain
terminal that has recently been constructed by the Dalian Beiliang Company
and is located just outside the city of Dalian in the Northeastern province
of Liaoning. Funding for the silo component of the project was jointly provided
by the World Bank and the Chinese government under the auspices of the World
Bank's Grain Distribution and Marketing Project. Approximately 150 x 3000
tonne silos have been constructed, plus 8 x 1400 tonne working bins, and
the facility has a planned throughput capability of some 9.3 million tonnes
per annum of corn exports and (mainly) wheat imports.

Only 27 x 3000 tonne silos plus 4 x 1400 tonne
working bins have been fitted with fumigation (too few to effectively control
insects in such a large facility, in the author's opinion, no matter how
good the fumigation system). Five separate fumigant distribution systems
were established, all fed from a central ECO2FUME® delivery system.

Instead of pre-mixed ECO2FUME®, GTS elected to offer site mixing
of CO2
and VAPORPH3OS® (PH3) as a means of
reducing fumigant costs and inventory of cylinders. The central mixing facility
incorporates a 5 tonne cryogenic liquid CO2
storage tank, a storage compound for ECO2FUME® cylinders, an electric vaporizer
for vaporizing the CO2 as it is delivered from the tank, and an automated
mixing system. Control of gas delivery and mixing, including automatic switching
from ECO2FUME® cylinder to another, is via a local PLC.

ECO2FUME is reticulated to each of five dispensers,
which control the flow-rate of ECO2FUME® into the ductwork where it is mixed
with an airsteam delivered from the adjacent fan. A SIROCIRC® controller
automatically adjusts the flow rate to maintain a constant concentration
of PH3 in the ductwork. The dispensers and mixing system were all developed
and supplied by GasApps Australia, while the VAPORPH3OS® gas was supplied
by Cytec Industries.

Delivery ductwork is connected to several
silos (up to seven in this case), and the airflow rate into each silo is
controlled such that near-equal distribution of fumigant is achieved in
all silos regardless of the state of filling or airflow resistance of the
silo contents.

Valves are fitted to the ductwork above and
below each silo to allow isolation of silos that are not required to be
fumigated. A condensation trap is provided above each silo to catch and
remove condensation during cold conditions, and so prevent it dripping back
onto the grain surface. Because the silos are not fitted with aeration ductwork,
special diffusers had to be designed to diffuse the fumigant into the grain
mass within each silo. Instead of on-floor diffusers normally used, GTS
elected to use external diffusers bolted to the silo hopper outlets.

Because of the high grain throughput rates
expected at the terminal, all five systems were designed substantially oversized
for normal SIROCIRC® operation. This was done to provide the capability
for fast fumigation of individual silos, and for this purpose, each system
has been designed with the capability of delivering high concentrations
of phosphine (>700ppm) in a short period of time (around 12 hours distribution
time) to any single silo. Fan and duct sizes are therefore much larger than
otherwise needed.

GTS completed installation of the fumigation
system in May 2000 but commissioning was delayed until September because
of late completion of other works. Commissioning is now practically (and
successfully) completed, a concentration of 100 ppm having been successfully
maintained for an 18 day period in 11 differentially filled 3000 tonne bins.
All 11 silos were sealed to a 3-minute sealing standard, with the result
that very high rates of PH3 recovery were achieved. Whilst the rate of ECO2FUME® consumption
was not specifically recorded, measurements taken indicate that the recovery
rate was in the order of 90 to 95% once stable recirculation conditions
had been achieved.

Dalian Dalian Beiliang Grain Terminal - Phase 2 Development

Coincident with finalization of its contract
to install the fumigation system for the Dalian Beiliang Phase-1 silos,
GTS won a second contract to install similar SIROCIRC® fumigation
systems in the Dalian Beiliang Phase-2 silos on behalf of the same owner,
the Dalian Beiliang Company.

The Phase-2 component of the project was financed
independently from the Phase-1 component, and used only Chinese funds. The
storage consists of 20 x 30,000 tonne silos - perhaps the largest silos
of their type in the world. Each bin is 32 metres in diameter with an eave
height of 45 metres. Floors are flat and each silo is fitted with eight
large fans delivering air to eight separate in-floor aeration ducts. Roofs
are in-situ concrete cones, and being designed for long-term storage, silo
construction has been designed to achieve a degree of gas-tightness suitable
for successful fumigation.

GTS's design includes an ECO2FUME® mixing and reticulation system identical
to the Phase 1 design, feeding only four dispensers - each dispenser connected
to five silos. Fumigation delivery ductwork is connected to the aeration
ductwork - with eight delivery points per silo. A single recovery point
is provided at the apex of each bin.

GTS completed its installation work in June
2000 but has not been able to undertake full commissioning yet due to non-completion
of other works. Preliminary commissioning has been conducted however, which
verified that the required air-flows and gas-flows can be achieved, and
no problems are expected when full commissioning is conducted.

Country Silo Projects

GTS has recently signed contracts to supply
35 fumigation systems to newly constructed storages in 31 depots the Northeastern
provinces of China. All storages are of the "squat silo configuration
(large diameter, short wall height), and most are in the range of 5,000
to 10,000 tonne capacity. It is expected that all silos will be sufficiently
gas-tight to justify the provision of SIROCIRC® fumigation systems.

At most sites, a single fan and dispenser
are sufficient to deliver fumigant to the storages, though at larger sites
two separate systems are being supplied. In all cases, the fumigant mixture
is being supplied pre-mixed in cylinders because of the difficulties of
delivering bulk CO2
to the mostly remote locations involved.

At the time of writing, seven of these systems
have been completed and several more are in the process of installation.

Chinese Fumigation Systems

Whilst GTS has concentrated its efforts towards
marketing and adapting tried and proven technologies from Australia, competing
technologies are being developed locally at great speed aimed at penetrating
what is a new and quickly-expanding market.

Whether or not GTS's early activities at Changping
really sparked this hasty activity is uncertain, but the evidence suggests
that it probably did, since shortly after the start of the Changping trial,
Chinese central government decided that all future grain stores should be
fumigated using gaseous phosphine as the fumigant. Thereafter a large number
of new firms were established to try to take a share the market. One at
least produced a working copy of the SIROCIRC® controller, however
without a proper understanding of the engineering behind it, its performance
was apparently short-lived and it is not believed to be in commercial production.

It appears that most of the Chinese fumigation
systems that are finding their way onto the vast number of new Chinese storages
that are currently being constructed, are based on the use of phosphine
generators that use tablets as the source of phosphine. How successful these
will prove in practice remains to be seen, but so far as is known, all of
the many varieties of Chinese phosphine generator are designed to produce
a high concentration of phosphine over a period of a few hours, and are
thus to be used for "one-shot" fumigations (with top-up capability).
They do not appear to be suited to extended delivery periods as would be
necessary for SIROFLO®-type fumigations. Their success is thus likely
to depend ultimately on the gas-tightness of the storages that they are
attached to, and/or the resoluteness of local grain storers and handlers
(still under government control) to contain the spread phosphine resistant
pests. As in most countries, their understanding of insect resistance appears
to be limited and while that continues to be the case, very little is likely
to happen in terms of a widespread and active approach to combating it.

GTS hopes that by introducing new fumigation
technology into China, it may serve to broaden the level of awareness of
the existence of such technology, and the benefits that it offers.

One of 5 "Dispensers" for
metering ECO2FUME® gas mixture
into an airstream delivered to a group of up to seven silos. The dispenser
enclosure includes an air-pressure gauge, fumigant regulator, flow control
valve, flow meter and electronic SIROCIRC® controller. Behind the cabinet
is the fan that recirculates fumigant through the silos.

Undersilo Delivery Ducting feeding
a "Diffuser" mounted to the hopper discharge (prior to installation
of valves and chutework).

Dalian Phase-2 Silos: 20 bins each 30,000 tonne capacity. GTS's CO2 storage -tank and ECO2FUME® on-site mixing enclosure
are dwarfed by the silos. Fumigant delivery ducting can be seen around the
lower part of each silo.